The overall aim is to study the differentiation of properties among different excitable tissues in different animals and in different stages of development within the same animal. The following research is proposed: (1) Two distinctly different inward current mechanisms are found in the immature egg cell membraneofa starfish. Their changes into the matured Ca or Na channels will be followed during the maturation after the fertilization of eggs. (2) The properties of the two inward current mechanisms will be examined in different animals such as in eggs of protochordate to see any systematic difference along with phylogeny. (3) Mechanism of transmission in the absence of spike will be examined further between the photoreceptor and the second neuron in a barnacle. (4) The development of the Ca dependent action potential will be examined in the flight muscle of a fruit fly and the study will extended to heat sensitive mutants.